Apparently, they’re still on good terms, at least according to a source at Us Weekly. Via Huffington Post:

They are really good friends still and speak all the time, but their schedules just made it too difficult and it fell apart. [Chmerkovskiy] has a lot of respect for her, but it just wasn’t working anymore.

I’m sure both parties will be fine. Ms. Upton was just named “Model of the Year”and has her film debutcoming soon. She’s got a lot going on for her.